In the Block Inspector, Design > Background > Source shows the following:
The available options are:
In at least 9 out of 10 cases, the user wants to set a background image.
I think there is room for improvement.
The default (preselected) option could be a static image:
It’s only one click when a user wants to set a video source or dynamic image.
But it’s always 2 clicks in any case when an image (static or dynamic) is required.
It also could be discussed if it makes sense to implement a global option to set which image type is set by default. I assume static images are used more frequently than static ones, so not sure if it would make sense.
The Image Block (via primary panel), on the other hand, has already a default selection: